The mystery of what lies beneath the fields of a Harpenden farm under threat of being turned into a secondary school has been partially solved after a geophysical survey.

And its findings pose questions about an earlier assessment by consultants hired by the county council, who dismissed the archaeological value of the site as being low.

Alexander Thomas, a PhD student at the department of archaeology and anthropology at the University of Bristol, has carried out a two-day survey at Batford Farm, off Common Lane.

Herts county council is keen to have a new six form of entry secondary school built on the Green Belt land where farmer Phil Holt’s pedigree cattle-raising business has been based for 15 years.

But 25-year-old Alexander, who grew up in Harpenden, wanted to find out whether remnants of historic structures could be detected under the pasture.

He said: “The site has the potential to confirm the origins of Batford Mill and help explain the shift in Harpenden’s settlement in the late-Roman and Medieval periods.

“This site is surrounded by others of historic importance and is one of the last remaining undeveloped riverside and greenfield spaces in Harpenden.

“The field has not been extensively ploughed, which means that any archaeology should be in good condition.”

Harpenden’s ancient heart is around the River Lea at Batford.

Following analysis of data collected during the survey, Alexander said: “The results strongly suggest the field does contain the remains of buildings shown in historic maps.

“This is an extremely exciting development as not only might we be able to ascertain the age of Batford Mill, but also the ancient origins of Harpenden.

“This can only happen, however, with further surveys and digging.”

Alexander is recommending that a full archaeological evaluation be conducted before plans for the proposed school are taken further, as his findings are “significant” and there is “now an urgent need to protect this site in Batford”.

Batford Farm itself was, according to the Tithe Award Map 1840, previously called ‘Bonny Boys Farm Homestead and orchard’.

Alexander said that description was significant as homestead derives from an Old England term meaning settlement.

He added: “Cartographic evidence and geophysics results agree that there are building remains in this field.

“Buildings associated with a Domesday recorded mill and in a field named ‘homestead’ increase the significance further.”